1. Technical Field
The present invention relates in general to a riser tensioner system used during the offshore drilling and production phases and, in particular, to a standalone liquid level sensing device for monitoring liquid level in a composite gas accumulator of the tensioner system. The proposed sensing device and methodology can be extended to any other pressure vessel for liquid level sensing.
2. Description of the Related Art
Risers are used in offshore oil and gas drilling and production for conveying drilling mud as well as production fluids through a subsea wellhead to a floating production platform, also known as tension leg platforms (TLP) or SPAR. Tensioners are employed at the platform to apply tension to the risers. During the drilling or production phases, a riser system is typically kept in tension in order to avoid structural instability of the drilling or production stackup. A typical tensioner comprises a telescoping piston and cylinder arrangement supplied with gas pressure from accumulators. Waves and currents cause the piston and cylinder to extend and retract.
In one type of tensioner design, the piston component comprises a barrel that slidingly engages the cylinder or other barrel. Each barrel has a closed end and an open end, the open end being in fluid communication with each other. The interiors of the barrels serve as the chamber for receiving gas pressure. A plurality of pistons may be utilized.
A fluid within the chamber provides lubrication to dynamic seals. Thus, liquid level inside the accumulator is critical to ensure effective lubrication of dynamic seals. By using the liquid level information inside the accumulator, gas volume can be measured. The gas volume can be used to provide damping stiffness for the riser tensioner system. A novel technique for monitoring the liquid level inside an accumulator is desired.